Old Ratio of Arjun and Vaibhav = 3:2
Arjun's old share = 53
Vaibhav's old share = 52
Rahul is admitted for 51 share, which he acquires from the old partners in their old ratio (3:2).
The sacrifice means Rahul's 51 share will be contributed by Arjun and Vaibhav in the ratio 3:2.
Arjun's sacrifice = 51×53=253
Vaibhav's sacrifice = 51×52=252
New share of Arjun = Old share - Sacrifice = 53−253=2515−253=2512
New share of Vaibhav = Old share - Sacrifice = 52−252=2510−252=258
New share of Rahul = 51=255
New Profit Sharing Ratio = 2512:258:255 = 12:8:5